Some 40 percent of 140 students and staff exposed to tuberculosis at Longmont High School have tested positive for latent TB, a rate that one expert called "absolutely astounding."

The unexpectedly high rate of positive tests means health officials now plan to test all the roughly 1,200 students and 120 faculty and staff who were at the school in the fall term, said Dr. Randall Reves, director of the of the Denver Metro Tuberculosis Clinic, based at Denver Health.

The testing started after a Longmont High student was diagnosed with active TB last fall. Health officials began by testing students who had two or more classes with the infected student. As positive results kept appearing, the circle of people who were tested grew.

Reves said the strain of TB that the student had is not drug-resistant, which he called "very good news."

In fact, a Boulder County public health official stated in an e-mail to Boulder County government employees that the student "is expected to make a full recovery" and return to school when health officials decide it's safe.

While contagious, TB is not easily spread, said Dr. Michael Iseman, a lung and infectious disease specialist at National Jewish Health.

That makes the high rates of infection at Longmont High all the more surprising, he said.

Reves said being in close quarters with an infected person facilitates transmission, and poor ventilation can also play a role.

St. Vrain Valley schools spokesman John Poynton said Reves has inspected ventilation in the 47-year-old building but did not report finding any problems.

A positive test result does not mean a person has active, contagious TB. It is possible for tuberculosis bacteria to be dormant for years without creating active disease.

None of those who tested positive appear to have active TB, Reves said. Nevertheless, they will be treated for the disease to prevent it from progressing.

"We've got staff up in Longmont today getting students on treatment," Reves said.

At the turn of the last century, TB was one of the leading causes of death among young adults in New York City, Iseman said. And many communities in Colorado and across the West got their start by marketing their dry, sunny climates as therapeutic for TB patients.

But in recent decades, TB has been rare in this country. Last year, there were just over 11,000 cases in the U.S., Iseman said.

TB vaccinations are used in many countries, but are considered somewhat ineffective and not used in the United States, he said.

Reves said blood tests for TB cost about $40 each, just for the equipment and processing, while the older skin test method costs considerably less. Still, the cost, which is being picked up by the public health departments, is expected to be significant.

"It's expensive, and the state knows this." But, Reves likened it to a wildfire — it's unexpected but for the public good, "you have to be able to respond."

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